Australian researchers believe they have discovered how some species of birds have developed the ability to understand each other's language.

Associate Professor Robert Magrath and colleagues of the School of Botany and Zoology at the Australian National University in Canberra, found that fairy-wrens have the ability to learn the alarm calls of other species, giving them the edge when it comes to escaping predators.

While it has been known that some species of bird use the alarm calls of others to flee danger, how they develop this ability has been unknown.

One hypothesis suggests individual species recognise other species alarm calls because they have an inate ability to respond to calls that are similar in acoustic structure.

Another possibility is that they learn the calls of other species over time.

To test which hypothesis was most likely, researchers played recordings of white-browed scrubwren alert calls to fairy-wrens located in Canberra where they are found living side-by-side. The alert calls of both species are similar, but not identical.

They then played the scrubwren calls to fairy-wrens located in the Macquarie Marshes, 600 kilometres away, where there are no scrubwrens.

"If [the response] is due to similarity, and you go to an area where fairy-wrens occur, but scrubwrens don't...and play back the scrubwren calls, they should still flee for cover," says Magrath.

The results show that the fairy-wrens in Canberra fled, but the Macquarie Marshes fairy-wrens didn't.

"That's consistent with learning," says Magrath.

To further test this hypothesis, the researchers played recordings of a New Holland honeyeater, which has a very different alert call.

"The fairy-wrens fled. They can learn calls that are totally different to their own," Magrath says.

Magrath and colleagues also played the honeyeater calls backwards to test whether fairy-wrens were responding to general acoustic features such as peak frequency or rapid repetition.

The results showed that almost all ignored the backward call.

"The fact that they don't respond shows that they have learned honeyeater's call and are not responding to some general acoustic property like rapid repetition," he says. "They have a very acute perception about other species calls."

Emergency pack

Professor Gisela Kaplan from the Centre for Neuroscience and Animal Behaviour at the University of New England in Armidale says the study is well constructed, but believes the flee response isn't entirely due to learning.

She believes the brain contains an "emergency pack" of pre-programmed responses at birth. This pack may consist of neurones that provide a basic reflex when triggered by auditory responses, she says.

"It could be that a certain sound, like a 6 kilohertz high-pitched frequency, is part of that basic reflex," says Kaplan.

"Where the learned part comes in is to then correctly distinguish whether somebody else is simply making a high-pitch call or if it is an alarm call."

Kaplan adds that unpublished research on magpie behaviour, suggests the location and distance of the calls can affect how the birds respond.

"We played the same sound to magpies at different distances and found the response was different," she says.

"It depends on whether the bird's sound is coming from within the magpie's territory. The difference can be as small as two metres."

Whatever the cause of the bird's ability to understand other species' alarm calls, Magrath believes the findings have implications for captive breeding programs.

He suggests handlers should teach individuals to recognise calls of other species, as well as their own, before they are released into the wild.